The present invention relates to electronic switching systems for telecommunications use enabling a reduction in matrix requirements and eliminating the necessity for all auxiliary access matrices. The reductions are effected without sacrificing service and without encountering an excess number of lost calls. The invention is especially applicable to systems using stored program control with a small to medium size computer or data processor controlling a matrix (preferably electronic) to permit automatic path completion responsive to marking of the matrix network ends.
Electronic switching system patents disclosing matrix networks of the type shown herein include, for example, U.S. Pat. Nos. 3,133,157 issued May 12, 1964 to E. Platt et al; 3,201,510 issued Aug. 17, 1965 to J. Bereznak; 3,204,044 issued Aug. 11, 1965 to V. E. Porter; 3,258,539 issued June 28, 1969 to N. Mansuetto et al; and 3,452,158 issued June 24, 1969 to N. Jovic. Each of these patents shows an electronic telephone switching system employing PNPN devices as crosspoints in an endmarked switching network. The network shown may be single stage or multiple stage networks of the end-marked type in which a mark is placed on both the line side and the supervisory side of the network responsive to a call having been initiated and a junctor having been allotted or selected to process that call. In response to the marks at both ends, one of a plurality of possible paths between the marked endpoints is automatically completed through the network between the marked points. On an incoming call, a like path is completed from the incoming trunk to the line side of the network to complete a path through the network.
Once a path has been established from a circuit on one side such as the line side to one supervisory side circuit, other supervisory side circuits may be necessary to provide call-processing functions. In each such case, the necessary function circuit is marked to complete a path from the new function circuit to the line circuit involved and the prior path can be dropped.
In U.S. Pat. No. 3,258,539 to Mansuetto et al, noted above, there is shown a system in which one network path is dropped when another path is completed through the network and the use of the first path is no longer necessary. In that system, when a trunk call is to be attempted, a first path from line to general purpose junctor is completed. When sufficient digits have been dialed into the control to determine that a trunk call is desired, a second path is completed from the calling line to an available trunk and the original path is dropped once the second path is completed. It is to this type of system that the present invention relates.
More recent U.S. applications, 264,567 filed June 20, 1972, and now U.S. Pat. No. 3,806,749 issued Apr. 2, 1974 and 264,568 filed June 20, 1972 both inventions of N. L. Jovic, and assigned to the assignee hereof, show matrix network configurations also usable herein.